There are known a number of fire and explosion detection systems. Examples of such systems employing UV and IR detectors are illustrated in the following U.S. Pat. Nos. 3,665,440, 3,653,016 and 4,270,613. U.S. Pat. No. 4,270,613 of the present applicant/assignee describes a particularly useful detection and suppression system which provides an output indication in response to coincident detection of UV and IR wherein the detection bands exclude the visible spectrum. A particular feature of the system described in U.S. Pat. No. 4,270,613 is immediate response to a detection for actuation of suppression apparatus. Discrimination is made between different types of detections in terms of the number of detections within a predetermined period in certain modes of operation. In such modes, simultaneous or near simultaneous detection by a plurality of detectors results in an increased response in terms of actuation of suppression apparatus.